A metal aluminum material is widely used in the electrode wiring of a semiconductor device typified by DRAM and the reflection film of an optical device since it has high conductivity and high optical properties. An aluminum film has been formed mainly by sputtering, deposition or chemical vapor deposition (refer to JP-A 2000-86673 and “Semiconductor Process for Beginners” written by Kazuo Maeda and published by Kogyo Chosakai Publishing, Inc., pp. 232-239). However, as these processes require expensive and large equipment such as a vacuum chamber and a high-voltage current apparatus, they are costly and it is difficult to apply them to large-sized substrates, which is industrially disadvantageous. Further, semiconductor devices are becoming finer in pattern or optical devices are becoming more complicated in shape. When an aluminum film is formed in a semiconductor device having a fine pattern or an optical device having a complicated shape by a conventionally known technique, a defect may be produced in the formed aluminum film, or step coverage may become short.
Meanwhile, methods of forming an aluminum film from a coating composition which comprises an aluminum compound or a complex of an amine complex and aluminum hydride have recently been proposed (refer to JP-A 2002-338891 and JP-A 2006-237392). Since these technologies do not require expensive equipment, they have a low film forming cost and a satisfactory step coverage even for a substrate having a trench with a high aspect ratio. However, as these compositions are unsatisfactory in terms of long-term storage stability in some cases, further improvement has been desired.